The present invention relates to tools for removing a pellicle from a reticle or mask on a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to a new and improved de-pellicle tool which is capable of removing a pellicle from a mask without touching the mask.
The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.
Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic or photolithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate.
Photoresist materials are coated onto the surface of a wafer by dispensing a photoresist fluid typically on the center of the wafer as the wafer rotates at high speeds within a stationary bowl or coater cup. The coater cup catches excess fluids and particles ejected from the rotating wafer during application of the photoresist. The photoresist fluid dispensed onto the center of the wafer is spread outwardly toward the edges of the wafer by surface tension generated by the centrifugal force of the rotating wafer. This facilitates uniform application of the liquid photoresist on the entire surface of the wafer.
Spin coating of photoresist on wafers is carried out in an automated track system using wafer handling equipment which transport the wafers between the various photolithography operation stations, such as vapor prime resist spin coat, develop, baking and chilling stations. Robotic handling of the wafers minimizes particle generation and wafer damage. Automated wafer tracks enable various processing operations to be carried out simultaneously. Two types of automated track systems widely used in the industry are the TEL (Tokyo Electron Limited) track and the SVG (Silicon Valley Group) track.
The numerous processing steps outlined above are used to cumulatively apply multiple electrically conductive and insulative layers on the wafer and pattern the layers to form the circuits. The final yield of functional circuits on the wafer depends on proper application of each layer during the process steps. Proper application of those layers depends, in turn, on coating the material in a uniform spread over the surface of the wafer in an economical and efficient manner.
During the photolithography step of semiconductor production, light energy is applied through a reticle mask onto the photoresist material previously deposited on the wafer to define circuit patterns which will be etched in a subsequent processing step to define the circuits on the wafer. Because these circuit patterns on the photoresist represent a two-dimensional configuration of the circuit to be fabricated on the wafer, minimization of particle generation and uniform application of the photoresist material to the wafer are very important. By minimizing or eliminating particle generation during photoresist application, the resolution of the circuit patterns, as well as circuit pattern density, is increased.
Reticles must remain meticulously clean for the creation of perfect images during its many exposures to pattern a circuit pattern on a substrate. The reticle may be easily damaged such as by dropping of the reticle, the formation of scratches on the reticle surface, electrostatic discharge (ESD), and particles. ESD can cause discharge of a small current through the chromium lines on the surface of the reticle, melting a circuit line and destroying the circuit pattern.
FIG. 1 illustrates a cross-section of a reticle 10, having a mask material layer 12 and a chrome pattern 14 provided in the form of the desired circuit configuration on the mask material 12. During a lithography process, an optically-transparent pellicle film 16, which may be covered on both surfaces with antireflective coatings 18, is typically positioned about 5-10 mm above the reticle 10 to prevent airborne particles 20 from falling on the reticle 10 and thus, damaging the reticle 10 and causing an imaging defect.
As shown in FIG. 2, the pellicle film 16 is tightly stretched on a sealed frame 17 which is supported on the surface of the reticle 10. After the exposure, the pellicle frame 17 is removed from the underlying reticle 10 typically by operation of a conventional, manual de-pellicle tool 24. The conventional de-pellicle tool 24 includes an elongated handle 25 on the end of which is provided a head 26 mounted on rollers 27. A lift pin 28 extends forwardly from the head 26. Accordingly, as shown in FIGS. 2-2B, the pellicle frame 17 is initially raised from the surface of the reticle 10 by resting the rollers 27 on the peripheral surface portion of the reticle 10 and inserting the lift pin 28 into a pin opening 22 extending into the pellicle frame 17. Next, as shown in FIG. 2B, the rollers 27 act as a fulcrum as the handle 25 is lowered to raise the pin lift pin 28 in the pin opening 22 and partially lift the frame 17 from the reticle 10. Finally, the pellicle frame 17 is typically manually grasped and completely removed from the reticle 10.
One of the problems associated with use of the conventional, hand-operated de-pellicle tool 24 to remove the pellicle frame 17 from the reticle 10 is that the rollers 27 frequently scratch the surface of the reticle 10 as the tool 24 is moved forwardly to insert the lift pin 28 into the pin opening 22. Accordingly, a device is needed for raising a pellicle from a reticle without scratching and otherwise damaging the reticle.
An object of the present invention is to provide a new and improved de-pellicle tool for removing a pellicle film from a reticle.
Another object of the present invention is to provide a new and improved de-pellicle tool which prevents scratching or other damage to a reticle during the removal of a pellicle film from the reticle.
Still another object of the present invention is to provide a de-pellicle tool which requires minimal contact of the tool with a reticle for the removal of a pellicle frame and pellicle film from the reticle.
Yet another object of the present invention is to provide a new and improved de-pellicle tool which utilizes multiple lift pins to simultaneously lift a pellicle frame completely from the surface of a reticle.
A still further object of the present invention is to provide a de-pellicle tool which facilitates ease in removing a pellicle frame from a reticle.
Yet another object of the present invention is to provide a de-pellicle tool which facilitates quick, easy, low-risk and efficient removal of a pellicle frame from a reticle.
In accordance with these and other objects and advantages, the present invention is generally directed to a de-pellicle tool for removing a pellicle from a reticle during the formation of circuit patterns on substrates in the fabrication of integrated circuits. The de-pellicle tool of the present invention comprises a support frame on which is mounted the reticle and the pellicle supported on the reticle. A pair of handle-actuated lift pins on opposite sides of the support frame are extended into respective pin openings in the pellicle frame, after which the handles are pushed downwardly to raise the lift pins and lift the pellicle frame from the reticle. Accordingly, no moving parts contact the reticle during the pellicle-removing procedure, preventing scratching or other damage to the reticle.